Adumbration

Dan Savage may have an angry way of saying it (Why does this house cost ...), but the implication is correct - zoning limits decrease the availability of housing to levels lower than the community would choose if left to their own devices. 

Lots of people want to live in Seattle, for many different reasons; fewer available spaces will tend to go to people who are more willing and able to pay higher prices for them.

To the extent that people are interested in housing prices in Seattle, policy that restricts supply results in higher prices for that which remains.